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Steam Hammer for Forge.                    129

tempered steel to whalebone. Our process then when tempering
by the aid of water is to raise the steel to c glass/ and then lower
it gently to ' whalebone.' Hardening in oil gives the c whaleboneJ
without passing through the ' glass' stage.

THE FORGE,

We shall now pass on to describe the turning out of very
heavy forgings, which include all articles too ponderous for smith's
work, and which are consequently made in the forge under a very
heavy Steam-hammer. Fig. 124 is a drawing of a hammer
suitable for general forge work, such as we are about to consider,
but, of course, extra large forgings would require special-sized
hammers.

The hammer in Fig. 124, Plate IT., has a falling weight of
five tons. After the careful account of the smith's harnmer there
will be -very little to say here by way of description. As before,
the outer valve is for the purpose of admitting steam (being
opened by a screw acting at the end of a lever), while the inner
valve controls the direction of flow, the exhaust passing upward.
The long hand-lever serves to move the distribution valve, and
the self-acting aim between it and the valve reverses the latter
as soon as the arm is moved by the tup on its upward travel.

The Furnace used hy the forgeman is very similar to that
shewn in Fig. 85. It is there called a Puddling Furnace, and
indeed * blooms' are to be made for heavy forgings just as in the
•case of puddling, the only difference being that they are built
from scrap iron instead of white pig. A pile of scrap iron is
heaped on a rough wooden tray, and is then put into the furnace.
Several of these piles being so placed and heated sufficiently, they
are then found stuck together. Withdrawing them, thus adhering, •
by means of very large tongs having a balance-weight on the
handle end, and supported at the middle by a crane, the blooms
are put under the hammer and well beaten together to form slabs.
It will be these slabs that we shall use to build up our forgings.
Fig, 125 shews an arrangement of furnace and cranes for heavy
forgings.

First we shall consider, in detail, the forging of a Double-
throw crank shaft of large size, the finished form of which is